Multistage frequency reducer



Dec. 31, 1940..

K. SC HLESINGER 2,227,019 MULTISTAGE FREQUENCY REDUCER Filed July 6, 1937 /nvento Patented Dec. 31, 1940 UNITED STATES A'iE'l OFFICE MULTISTAGE FREQUENCY REDUCER Application July 6, 1937, Serial No. 152,001

In Germany July 8, 1936 1 Claim.

Multistage frequency reducers are required in the construction of electrical synchronisation generators for television. In my application Ser. No. 92,153 of July 23, 1936, there is set forth 5 an apparatus of this nature, in which the frequency reduction is performed with pentodes which oscillate at the lower frequency and the intercepting grid of which is excited by the higher synchronising frequency.

The difliculty arises that the frequency reducers perform synchronisation only when the synchronising potential has a certain definite amplitude value. This value depends on the characteristic of the controlled stage insofar as in the case of a smaller value the synchronisation will not work at all, whilst in the case of an over-excitation the oscillations generated in the controlled stage is disturbed and altered in frequency.

It is necessary, therefore, to provide a coupling between the two stages of the frequency reducers which fulfills two conditions:

1. In the case of zero coupling both circuits the synchronising circuit and the controlled one, must oscillate at their natural frequencies without influencing each other, so that it is possible to tune them approximately to the proper ratio before coupling them.

2. It must be possible, to increase the coupling 30 from zero continuously upto the value at which the synchronisation takes place without altering the natural frequency of either oscillator.

The invention is more clearly explained in the accompanying drawing in which i Fig. 1 shows a diagram of the circuit connection of two frequency reducer stages according to the present invention, whilst Fig. 2 shows a modification of this diagram.

In Fig. 1 there is shown a connection of this kind Which has been found to be very suitable in practice. The controlled oscillator is a pen tode I, having a control grid 1, a screening grid 8 and an intercepting grid 9. It oscillates with the frequency of its grid circuit. In order that this frequency will depend as little as possible on the mains potential the generator I produces its grid bias itself by means of a cathode resistance 4 shunted by a condenser 5. In order that the amplitude of the oscillation is limited and that its frequency depends as little as possible on the individual properties of the tube there are provided a grid-current limiting resistance 6 and an anode-current limiting resistance. 18. The potentiometer I9, 20 of the screening grid is not connected to the cathode 4, but directly to earth,

so that the anode current of the tube I is to a large extent independent of fluctuations in the mains potential. The resistance 20 is, for avoiding humming, shunted by a condenser 21.

The synchronising potential is conducted to the intercepting grid 9. Since the currents taken up by the intercepting grid have considerable influence on the frequency, there is connected a limiting resistance It in series to it. Its bias is, via a resistance ll, equal to that of the oathode- The synchronising potential is derived from the anode circuit of the preceding stage 2. In series with the reaction coil [21) of this stage, which oscillates at an n times higher frequency, is a potentiometerv l4. Its slider is connected by a coupling condenser 15' to the intercepting grid circuit H], II of tube 1. By moving the slider the coupling between both oscillators can be varied from zero to a sufficient degree.

For fine adjustment of the frequency of the circuits l2a, 3 (and 12a, 3) there is employed a small resistance It (resp. It) in series with the inductance. The direct current is kept oil at least from coil 12b having an iron core by means of a coupling condenser ll.

If all coils 12b are blocked by condensers, they may according to Fig. 2 be connected in series with the potentiometers M, instead to the positive pole of the mains, to the cathode of the next stage. This connection avoids that ripples and humming noises or traces of oscillations are transmitted from the anode of one stage to the next one. i

I claim:

A frequency changing apparatus comprising a first thermionic tube having an anode, a cathode and a grid electrode, an oscillation circuit comprising serially connected inductance and variable resistance elements and a capacity shunted across said serially connected elements, said oscillation circuit being connected between said grid electrode and the cathode of said tube, an inductive member connected in the anode; cathode circuit of said tube and coupled to the inductance element of the said oscillation circuit, potentiometer means connected in series in .said anode-cathode circuit, an impedance momhaving an anode, a cathode, a plurality of grid electrodes, means for impressing signals developed across the last named resistance means between one grid electrode and the cathode of means connected in the anode-cathode circuit of said second thermionic tube and coupled to the inductive means contained in said second oscillation circuit, said first oscillation circuit and said second oscillation circuit being tuned to harmoni- 5 cally related frequencies.

KURT SCHLESINGER. 

